I've been playing this game for over a year, mostly on the competitive speedrunning side of the community. Here are a few ideas I've thrown around on #dlc-suggestions in the Necrodancer Discord:

Shovels

Right now, I have two qualms with shovels:

All of the DLC shovels are titanium-but-better.

Score running has been made significantly more RNG-dependent since it's harder to find the blood shovel.

One suggestion is simple - nerf Shovel of Courage to base dig level. This is currently the strongest shovel for speedrunning, and this nerf would be thematically fitting with the Ring of Courage's +1 damage removal.

The other suggestion is a new Gold Shovel. I've spent a great deal of time mulling over how to balance such a shovel for score, and here's what I've come up with:

Acts like a basic shovel normally.

The beat after picking up gold, you can dig any wall, but at the cost of the gold you just picked up. This prevents you from easily clearing out shop walls in score runs - you have to kill enemies against the wall and use their gold to dig the shop out.

The shovel needs some kind of big dig à la Blood Shovel to be worthwhile for score runs - but the standard big dig would let you get half the gold from every shop, since each dig parallel to the wall would dig out two more shop walls. Hence I'm proposing the gold-charged digs be broad digs - they dig out all the walls in broadsword range. If you try to dig parallel through the shop walls, you only get one wall at a time, so no net gold except around corners. But luring enemies to the wall lets you dig 3 shop walls at once.

If this is still too weak for score, the shovel could also give extra gold from walls (maybe +2 or even double). This would also apply to the one wall tile that contains 25 gold on each floor. This still wouldn't make parallel shop digging viable since the digs would consume the extra gold as well.

The shovel is still valuable for speedruns / casual runs since it gives you a way to open any locked shop.

I'd like to see more shovels that can dig catacomb walls, or can only dig dirt walls under normal circumstances, but for now I think these two changes would greatly diversify the shovel pool and make score running a little less painful (and maybe even more fun!).

Reverse Zones mode

To my understanding, Aria's zone reversal was implemented mostly for lore purposes, and most serious players aren't fond of it. Here's what I propose as a compromise:

Add a new gameplay mode for reversed zones that any character can use. Story characters would get their final bosses at the end of Zone 1, the same way Aria works currently.

Change Aria's All Zones to standard zone progression.

Keep zone reversal for Story Mode. Story Mode would then be summarized as Cadence All Zones, Melody All Zones, and Aria Reverse Zones. This preserves the lore and hopefully satisfies the players who are irked by Aria's difficulty curve.

Seeded teleports

Too many races are decided by who gets good teleports from locked shopkeepers (esp. in the early game when throwing is the only way to kill), magic monkeys, and the Necrodancer boss. All of those entities can only teleport a limited number of times, so it should be viable for those teleports to be seeded. You could use the same algorithm that conjured items / mommy babies use to break ties if the spawn location is already occupied. There are some other less decisive teleports, like Crown of Teleportation on boss floors and the Dove Familiar, that I wouldn't mind staying unseeded for technical reasons, but having the 3 kinds of teleports listed above be the same every time would eliminate a great deal of the luck factor from races.

Attacks from silhouettes

If a Yeti was silhouetted the beat before it attacks you, the attack is cancelled. This was presumably added because Yetis are one of the few normal enemies* that can move and deal splash damage, which would lead to unfair situations around corners and when digging through walls. But there are other ways for a silhouetted enemy to attack you on the next beat, mainly involving Boots of Leaping, Lunging, or diagonal movement (Diamond or Zone 4 bouncetraps). I propose that no invisible or silhouetted enemy should be allowed to hit you on the next beat, not just Yetis. I've had very few deaths that I would call truly unfair in this game, but about half of the ones I can remember involved enemies attacking me the same beat they became visible.

* Mushrooms deal splash damage but don't move; Coral Riff's head and FortissiMole both deal splash damage and move, but are bosses and as such aren't unexpected.